The present invention relates to a disc brake assembly including a pad retainer having a planar region situated at a first radius that engages a planar region of a pad spring to restrain radial movement of a brake pad and the pad retainer is secured to an outboard side of a brake caliper at a second radius, and the pad retainer has a crook that allows the second radius to be less than the first radius.
Known disc brakes 10 (shown in FIGS. 1 to 4) include a disc or rotor 20 mounted to a wheel hub for rotation wit a vehicle wheel. A brake carrier 12 is fixed relative to the axis of rotation of the rotor 20 and is secured to a non-rotating portion of the vehicle (e.g. the vehicle suspension). In “floating caliper” type brakes, a brake caliper 15 including a bridge 16 secured to a housing 14 is slidably mounted on the brake carrier 12 to allow for movement parallel to the axis of rotation of the rotor 20. An actuator 18 communicates with one or more pistons or tappets (not shown) provided in the housing 14 to apply the force required for the brake to function.
A pair of brake pads 22 including friction material 36 mounted to a solid backplate 34 are positioned on either side of the rotor 20. The friction material 36 faces the planar faces of the rotor 20. The backplates 34 of the brake pads 22 are seared on vertical and horizontal abutment regions 28 and 30, respectively, provided in openings 32 in the brake carrier 12 to restrain the brake pads 22 from rotational and radially inward movement, respectively. In a typical “floating caliper” type brake, one of the backplates 34 engages with the piston(s), either directly or via a spreader plate, to distribute the load. The actuator 18 causes the piston to push one of the brake pads 22 towards the rotor 20 to achieve braking. Because the caliper is able to “float” on the brake carrier 12, an equal frictional braking load is applied by both brake pads 22.
The backplates 34 of vehicle disc brake pads 22 perform two functions. First, the brake pads 22 provide a solid support for slidably mounting the friction material 36 of the brake within the brake carrier 12 to transmit the shear loads induced on the friction material 36 during braking to the brake carrier 12. Second, the brake pads 22 transmit and evenly distribute the pressure applied by the brake tappets or the pistons during braking to the surface of the friction material 36 to ensure even wear of the friction material 36. To perform the functions, resilient members (such as a leaf type pad springs 24) are commonly used to restrain radially outward movement (indicated by arrow R) of the brake pads 22 in the brake carrier 12 while permitting movement towards and away (indicated by arrow A) from an associated brake disc and to prevent rattling of the brake pad 22 in use.
The pad springs 24 are typically elongate and, when fitted, extend along a portion of the radially outermost face of the backplate 34. The pad springs 24 are typically pre-loaded to a certain extent against the brake carrier 12 by a pad retainer 26, which spans an opening between the bridge 16 and the housing 14 and contacts the approximate center of the pad spring 24. This force is typically reacted radially outwardly by contact of the backplate 34 with each end of the pad spring 24. Formations are also typically provided on the backplate 34 and/or the pad spring 24 to retain the pad spring 24 on the backplate 34 during movement of the brake pad 22 parallel to the axis of rotation of the rotor 20.
During brake actuation, the backplate 34 and the pad spring 24 move toward and away from the brake disc. If the pad retainer 26 and the pad spring 24 are not parallel (due to loads on the pad spring 24 and/or uneven brake pad 22 wear), the edge 25 of the pad spring 24 tends to indent into the underside 29 of the pad retainer 26, preventing movement of the backplate 34 and inhibiting braking performance. This problem is increased when heavy brake pads are used because a stiffer pad spring is required, which has a greater tendency to indent into the pad retainer 26.
Great Britain patent applications GB2356027, GB2172352 and GB2142394 describe typical known brake pad springs which are made from wire and used to prevent radial movement of a brake pad.
German patent applications DE3222859 and DE3227195 both describe a disc brake pad assembly including pad springs with rounded edges which abut against a pad retainer to restrain radial movement of a brake pad.